java - 处理 Applet 抛出 java.lang.ExceptionInInitializerError 并阻止其运行

Question

我们正在开发 Java 小程序并将其嵌入到我们的网页中。当通过 HTML APPLET 标签加载 applet 时，浏览器/JVM 会提示用户允许它运行。当我们点击取消时，java 控制台会显示以下异常:

java.lang.RuntimeException: java.lang.ExceptionInInitializerError
    at sun.plugin2.applet.Plugin2Manager.createApplet(Unknown Source)
    at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.ExceptionInInitializerError
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source)
    at java.lang.reflect.Constructor.newInstance(Unknown Source)
    at java.lang.Class.newInstance0(Unknown Source)
    at java.lang.Class.newInstance(Unknown Source)
    at sun.plugin2.applet.Plugin2Manager$12.run(Unknown Source)
    at java.awt.event.InvocationEvent.dispatch(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$000(Unknown Source)
    at java.awt.EventQueue$1.run(Unknown Source)
    at java.awt.EventQueue$1.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)
Caused by: java.security.AccessControlException: access denied (java.lang.RuntimePermission getenv.TEMP)
    at java.security.AccessControlContext.checkPermission(Unknown Source)
    at java.security.AccessController.checkPermission(Unknown Source)
    at java.lang.SecurityManager.checkPermission(Unknown Source)
    at java.lang.System.getenv(Unknown Source)
    at downLoadApp.<clinit>(downLoadApp.java:15)
    ... 21 more
Exception: java.lang.RuntimeException: java.lang.ExceptionInInitializerError

现在，我意识到这很可能是因为 java 试图加载的类被阻止加载，因此抛出了异常，但是我们如何在浏览器中优雅地处理这种情况？我想检测小程序被拒绝并对这种情况发布合理的响应，但我不知道如何捕获此异常，因为它似乎是由 JVM 抛出的，以响应未获取 jar 文件的情况加载而不是其中编写的代码...

想法？

谢谢!

Answer 1

您可以通过在 try-catch 语句中调用 downLoadApp.java 第 15 行中的 System.getenv 来捕获访问控制异常。也就是说，而不是这个:

static String tmp = System.getenv("TEMP");

你应该有:

static String tmp;

static {
    try {
        tmp = System.getenv("TEMP");
    } catch (java.security.AccessControlException ace) {
        // tmp is not set, maybe use some default value?
    }
}